Generally, polymer particles can be manufactured from a polymer latex, for example, by adding a coagulating agent to the polymer latex, and spraying and drying the polymer latex in hot-air.
In the above-mentioned method of coagulating particles by adding the coagulating agent, many processes such as a coagulation process, a washing process for removing the coagulating agent, a dehydration process, and a drying process will be needed to collect the polymer particles. Accordingly, this method has problems of high facilities cost and complex operation control.
In the above-mentioned method of spraying and drying the polymer latex in hot air, the polymer particles are obtained by atomizing the polymer latex into a dryer. The polymer particles are obtained by evaporating water from whole surfaces of the atomized polymer latex, by forming film layers on their surfaces, and drying. Using this method, the polymer particles can be obtained from the polymer latex by a single process. This method is superior industrially, because it has low facilities cost and easy operation control.
However, if a polymer latex having a higher minimum film forming temperature is dried in hot air, some hard film layers formed on the surfaces of polymer latex particles will be broken. If these film layers are broken, the particles themselves will also be broken, and minute particles will be formed. Therefore, many minute particles tend to be contained in the polymer particles obtained by drying the polymer latex. These minute particles often cause dust, and it deteriorates powder handability of polymer particles.
Further, if a the dryer outlet temperature is raised to avoid the breaks of the polymer latex particles in the spraying and drying, the amount of adhered particles on the wall surface and the cone part of the dryer will be increased, and the polymer particles will clog at the outlet of the dryer.
JP-A No. 63-190601 describes a method of spraying and drying wherein a solution or slurry is dried using heated gas having more than 20% of partial pressure of superheated steam. By this method, when a solution or slurry containing inorganic compounds is used, concentrations of components exist in a particle can be equalized and heat efficiency can be raised. However, this document has no description about a polymer latex, a method of preventing from forming minute particles, and a method of decreasing the adhering and the clogging in the dryer.